The rationale for these studies is to explore the role of the bronchial circulation and vascular volume and permeability in the production and/or attenuation of airway obstruction induced by various stimuli i.e. exercise, hyperventilation, allergen, and methacholine. Bronchial blood flow is manipulated by saline, dextran, or dextrose infusions; intravenous or inhaled diuretics, inflation of the lower limb bladders of anti-shock trousers, inhaled vasoconstrictors and vasodilators, or standard anti-asthmatic agents i.e. parasympatholytics, beta agonists, and mast cell stabilizers. The results of these maneuvers upon airway function and reactivity are then assessed. Finally, intra-airway temperatures, as a reflection of flux in blood flow within the bronchial circulation, are measured prior to and following these manipulations in an effort to determine whether alterations in reactivity are indeed correlated with changes in vascular congestion.